Positive crankcase ventilation (PCV) vapor contains a large fraction of water. The water vapor can condense on the cold air duct walls and the interior of the intake manifold walls. Further, the PCV vapor may freeze into ice downstream of the PCV port in the cold air duct. Following a day/night cycle, the ice melt may drip and/or drain down to the lowest spot of the intake system and re-freeze. Once the engine is restarted, blow by flow moving downstream to the turbocharger or throttle body may dislodge the ice and move it downstream causing the icicle to be ingested by the turbocharger or throttle body. Dislodging of the ice may result in turbocharger blade damage or blocked throttle bodies thereby creating noise, vibration, and harshness (NVH) and/or lack of power in the engine.
Patent WO2012157113 describes an approach with the use of a capture member in an intake structure upstream of a compressor impeller. The capture member includes a circular mesh plate formed in an intake passage to capture ice formed in a blow-by gas passage.
The inventors herein have recognized the above issues as well as issues with approaches such as described in WO2012157113. For example, accumulation of ice on the mesh plate may limit the amount of airflow into the compressor, thereby reducing the efficiency of the engine. Further, the mesh plate may not capture all of the condensate and engine operation may be reduced due to condensation in the intake air.
In one example, some of the above issues may be addressed by an engine air intake duct, comprising an air intake duct wall including an ice ingestion feature positioned at a bottom of an engine air intake duct wall and a positive crankcase ventilation outlet coupled to the air intake duct wall upstream from the ice ingestion feature. Further, the ice ingestion feature may be formed by a plurality of indents where at least two indents contain a different volume. In this way, it is possible to retain positive crankcase ventilation condensation. Further, the condensation may be retained in the ice ingestion feature based on an ice retention rate determined by the geometry of the indents.
In another example, a method for retaining ice in an air intake duct, comprising flowing crankcase gas from a PCV port to an air intake duct upstream of an engine cylinder and collecting condensate in a plurality of indents positioned in a bottom wall of an air intake duct. Further, the method includes collecting condensate in the indents (e.g. compartments), thawing them during engine operation at different rates, and ingesting water from the compartments at different engine cycles. In this way, the condensation may be more slowly ingested by the compressor without damage to the impeller blades or blocking the throttle plate from closing.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.